This invention relates generally to a process for the specular metallization of a substrate and the article produced thereby. The substrate may be in web or sheet form and may consist of paper, cardboard, wood, plastic and many other substances. A highly glossy, smooth, polished specular metal appearance is conferred to the substrate without the necessity for the substrate to be specially treated, or polished.
In the art, various processes are known for the metallization of a substrate surface in web and sheet form. One process involves the lamination of a metal foil to a substrate by the use of solvent based or polymerizable adhesives. This process is commonly used for the metallization of flexible materials and the most common metal used is aluminum foil. The process requires that the metal foil be of a thickness of more than 1 micron. The use of thinner foils is not possible on a mass production basis and is only possible in small batch production. In order to obtain a specular finish, the metal foil must have a polished finish. The gloss and finish of the final product do not depend on the substrate but rather, on the gloss and finish given to the foil.
Another known process consists of the dispersion of extremely fine metal powder in a binder and a spreading of the binder containing of the powder over the surface to be metallized. Further metallization processes are carried out by chemical precipitation and electrolytic means. In these processes, the gloss and finish of the metallized surface depend on the gloss and finish of the substrate. A high gloss and specular finish is obtained when the substrate materials are glossy, such as a plastic film or a polished surface. Where the substrate is not smooth, a smooth finish will not be obtained. Accordingly, in these processes the gloss and finish depend on the finish of the substrate rather than the metal used.
A further commonly used process is vacuum metallization, in which vaporized metal is condensed on the substrate to be metallized. This requires that the substrate be placed in a chamber under a high vacuum of the order of 10.sup.-3 ` 10.sup.-4 `torr. Clearly, this process is restricted to materials which will not degas or contain volatile substances such as moisture, plasticizers and resins. A disadvantage of this process is that the resulting surface is generally fairly rough since the vaporized metal does not even out the roughness of the surface onto which it is condensed. To improve the finish of a substrate such as paper, it is necessary to pre-polish or pre-varnish the paper substrate. In certain instances, even pre-treatment is insufficient to produce a specular surface and a further step of calendaring the substrate surface at a high temperature is necessary. This extra step considerably increases the cost of the finished product.
Furthermore, when this process is utilized with materials that substantially degas, such as paper and cardboards, vacuum metallization equipment capable of attaining a high vacuum is necessary to overcome the loss of vacuum in the chamber caused by the air and moisture contained in the paper or board. In some instances, degasing of the material may be required prior to metallization.
The instant process and article produced thereby are directed to providing a smooth specular surface that is independent of the smoothness of the substrate or the metal, without the need for pretreatment of the substrate and without exposing the substrate to a vacuum.